1. Field of this Invention
This invention relates to a bolometric radiation detector, which consists essentially of a thin, temperature-sensitive, electrically-conductive measuring layer and to a method of producing the detector.
2. Prior Art
Thermal radiation detectors for the infrared range are indispensable for many applications in spite of the great advances that have been achieved in the field of cooled quantum detectors. The advantage of thermal radiation detectors is the independence of their radiation sensitivity from the wavelength and the ambient temperature.
Various types of radiation detectors are known. Those that utilize the pyroelectric effect of certain crystals can only be successfully used when on the one hand the ambient temperature is sufficiently below the Curie temperature of the crystal and on the other hand the variations in the ambient temperature do not exceed a specific value of about 0.5 K/minute.
Due to their simple and robust design, thermocouples and bolometers are preferred. The bolometer has the further advantages of constant sensitivity over the whole detector surface, the possibility of higher impedance and the reduction of the settling time by means of a rise in the working temperature.
The bolometer is normally a blackened, tape-like conductor made of a metal with a temperature-coefficient of electrical resistance that should be as high as possible. The change in resistance as a result of heating up by radiation is measured using a bridge circuit. Gold is a favorable conductor material since it is easy to work. Pure metal conductors have the significant advantage that the sensitivity of the detector (signal-to-noise ratio) is limited only by the Johnson noise of the bolometer resistance. All other parameters remaining equal, the signal-to-noise ratio is independent of the ohmic resistance of the bolometer. However, the signal level is dependent on the radiation concentration, i.e., on the square of the image scale of the light source onto the bolometer. In the manufacture of bolometers according to conventional methods, there are mechanical limits which have to be respected in the required reduction in the size of the bolometers. As a result, with even moderately small dimensions the internal resistance becomes too small, the heat capacity and thus the settling time becomes too large, and the heat dissipation via the mounting of the bolometer strip becomes much too high.